1. Field of the Invention
The present invention relates to a magnetic recording medium, in particular to a photo-magnetic recording medium that can reproduce information signals with magnetic domain wall displacement reproducing system and a method for manufacturing the medium.
2. Related Background Art
Various methods to reproduce information signals stored in magnetic storing media are conventionally known. In particular, a magnetic wall displacement reproducing system that the present applicant hereof proposed in Japanese Patent Application Laid-Open No. 6-290496 is to enable information signals with high resolution capability by using displacement phenomena of the magnetic domain wall. That is, using magneto-optical medium in which information signals are formed by the magnetic domain wall on a belt-shaped recording tracks, heating the recording tracks with irradiation of the reproducing light beam to form a movable region without the magnetic domain wall being restrained and as a result driving force by inclination of temperature is operated onto the magnetic domain wall to move it at high speed, and detecting that movement, reproduction of the information signals is implemented.
FIGS. 6A and 6B are partially enlarged views of configuration of a conventional magneto-optical medium 31 used in such magnetic domain wall displacement reproducing system. FIG. 6A is a longitudinal section while FIG. 6B is a plan view. In the figures, magneto-optical medium 31 is comprised of a substrate 32 which is made of transparent resin material such as polycarbonate and configured so as to have belt-shaped portions so that grooves G and lands L are alternately formed in parallel, a magnetic layer 33 formed on the substrate 32 and comprised of a magnetic material, and a protection coat 34 comprised of ultraviolet-curing resin. The magnetic layer 33 provided on land L comprises a belt-shaped recording track RT on which information signals are recorded. The magnetic layer 33 is formed by laminating three layers made of magnetic materials, for example, transition metals such as Tb, Gd and Dy, that is, a displacement layer 33a, a switching layer 33b, and a memory layer 33c. Here, the displacement layer 33a is a perpendicular magnetization film having magnetic coercivity smaller than that of the memory layer 33c and a domain wall mobility larger than that of the memory layer, the switching layer 33b is a film of a magnetic material having curie temperature lower than that of the displacement layer 33a and the memory layer 33c, and the memory layer 33c is a perpendicular magnetization film.
In addition, the magnetic layer 33 formed on a bottom surface and a side surface of a groove G is a sectioning region S in which the perpendicular magnetic anisotropy has been lowered (hatched-portions in FIGS. 6A and 6B). The recording track RT and the sectioning regions S at the both sides of the recording track do not undergo magnetic coupling or do undergo magnetic coupling to an extremely small extent. Such sectioning regions S are formed by being heated with a highly powered laser beam radiation to the grooves, or by a method such as dry etching.
When information signals are recorded onto the recording tracks RT of such magneto-optical medium 31, with the sectioning regions S having been provided in the both sides of the recording tracks RT, the magnetic domain wall, which is a recorded domain, is formed so as to span both ends of the recording track RT without being closed. Accordingly, irradiation of the reproducing light beam makes the magnetic domain wall displace easily, whereby magnetic domain wall displacement reproduction is made to be possible.
In the above described magneto-optical medium, the information signals are recorded only in the recording tracks RT, and the information signals cannot be recorded in the sectioning regions S comprised of magnetic layers 33 with poor magnetic feature. Accordingly, in order to increase the recording density of the information signals, it is effective to narrow the width of the sectioning regions S to increase track density. In conventional ways, in order to form the sectioning regions S, a method of removing a magnetic body by etching and a method of annealing a magnetic body with a laser beam have been employed. However, the etching could not prevent metal contamination from taking place on the magneto-optical medium. In addition, the laser annealing could not narrow the width of the sectioning regions because a method of converging the laser and the conditions for convergence were not optimized.
An objective of the present invention is to provide a magneto-optical medium of a magnetic domain wall displacement reproducing system, which has a recording density not less than in a conventional method by optimizing irradiation conditions of a laser at the time of forming sectioning regions to narrow width of the sectioning regions, as well as manufacturing method of the medium.
The above described problem is attained by a manufacturing method of magnetic domain wall displacement type magneto-optical medium comprising:
the step (A) of forming a magnetic layer all over a substrate; and
the step (B) of forming sectioning regions in which perpendicular magnetic anisotropy of the magnetic layer is reduced and by a plurality of belt-shaped recording tracks which are sandwiched from both sides of the belt-shaped recording track by the sectioning regions and magnetically separated from each other by irradiating the manetic layer on the substrate with a light beam or a charged particle beam of a wavelength of not more than 550 nm in the direction of from the opposite side of the magnetic layer from that facing the substrate toward the substrate and scanning the converged energy beam on the substrate in parallel and at a same interval.
In addition, the above described objective is also attained by magnetic domain wall displacement type magneto-optical medium manufactured with the above described manufacturing method.
Detailed description will be given in examples described later.